The present invention relates to a solenoid operated bypass valve and a relief valve, and more particularly, to a cartridge valve assembly including both the bypass valve and the relief valve.
It is well known to those skilled in the art to provide a hydraulic pump with some sort of valve arrangement, such as a bypass valve or an unloading valve, etc. whereby the output of the pump will be communicated to a fluid pressure actuated device under certain operating conditions, but will be diverted from the fluid pressure actuated device under certain other operating conditions. Typically, the fluid which is diverted from the pressure actuated device (i.e., a hydraulic motor, cylinder, etc.) is directed to the system reservoir, or back to the inlet of the pump, or to some other similar low pressure "source" of fluid.
An example of a system of the type described above is on a construction vehicle such as a skid steer loader which has, in addition to the hydraulically operated propel system, two or more hydraulically operated attachments, wherein at least one of the attachments requires a relatively low flow, and at least one of the attachments requires a relatively high flow.
In a known system, a primary pump is provided which alone can satisfy the needs of the low flow attachment. However, in order to meet the flow requirements of the high flow attachment, an auxiliary or secondary pump assembly is added to the vehicle, with the output of the auxiliary pump supplementing the flow output of the primary pump when the vehicle operator wishes to utilize the high flow attachment.
In order to keep such systems as simple as possible, it is necessary for the auxiliary pump assembly to be equipped with a bypass valve, a relief valve, and typically also a check valve to prevent "reverse" flow from the primary pump back through the secondary pump. Unfortunately, the addition of these various valve elements adds substantial cost to the secondary pump assembly, especially if each of the three valves mentioned is plumbed separately. The result may be a secondary pump assembly which is not economically feasible for a number of different vehicle applications.
For some vehicle applications, the auxiliary or secondary pump assembly is offered as a vehicle option, in the form of a "high flow kit", including the secondary pump and the associated valving. When the secondary pump is part of a kit, and is intended to be installed either by the vehicle dealer, or perhaps even by the ultimate customer, it is important for the kit to be as small and compact as possible, and involve as little plumbing as possible, thus minimizing the opportunity for assembly errors, leakage, etc.